I am long-winded, so please bare with me!
We are having trouble opening pdfs on certain websites. Currently PDPworks as well as one of our vendors who uses twelvehorses.com as a pdf server.
We are unable to open a pdf from pdpworks at all and are hit and miss with opening pdfs from twelvehorses.com.
The PDPworks scenario has been tested thoroughly with Adobe Acrobat 6.0 Standard, Adobe Acrobat 8.0, Adobe Reader 8.0, Adobe Reader 9.0 - all fully patched and updated and on various computers all running Windows XP. We have also tried used both Firefox 3.5, IE7, and IE8. No combination of the above have worked so we are pretty certain the issue lies within our network.
The second issue hasn't been tested as thoroughly with different browsers and what not since we're pretty sure there is an issue in our network somewhere and we're not sure if it is our DSL modem or our firewall.
What we have noted with the second issue is that sometimes the pdfs from twelvehorses.com will open right away and other times we have to try opening the pdf several times before it will load.
Our network administrator has been in contact with our ISP as well as Cisco support. Both have reviewed logs and confirmed that their products are not causing the problems (or at least that is what they're saying).
I also tried a computer that was removed from the domain to make sure it isn't a group policy issue and this computer couldn't open the pdfs either.
We also tried turning off windows firewall just to see if that might cause an issue.
So far no luck.
Any ideas or suggestions? Is there a program out there that will monitor network traffic usage from a specific pc and show us what the pc is getting in response from the firewall and remote website when a pdf is requested?
There are no internet explorer errors or other system or application errors in the event viewer.
Thanks in advance for any help!
Erin0201 :)

Try another PDF reader like FoxitReader if you can. Also clear all temp & cache files. Check for BHO add-ins (browser helper objects) that may be causing a conflict. Disable them and see if that changes any behavior.

(Edit)
Just in case anyone else has a similar problem.

The problem was between the ciscos PIX firewall and the new HP ProCurve switches that were installed. The autosensing ports were not connecting correctly. Once we set the ports between the two to full duplex everything worked fine. We’re in the process of setting everything we have to full duplex rather than autosensing so this doesn’t happen in the future with other devices. We’re hoping it will also improve our network speed by helping create less packet loss.

Thanks everyone!
Erin0201

Completely agree with this!! especially the first part of it. Not so up on the last part, but by simply changing your browser and clearing your cache files seems to help with the ensuing problems you were having.

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The download says it's going to take 30+ minutes to download 240kbs and then errors out. We had someone from Cisco say that it looks like the computer here is talking with the server and they both agree to make the connection and agree to close the connection several times when it should only happen once on the initial request. The packets just never come across. We're not quite sure what's going on yet. The DSL modem is setup as a bridge and so everything goes through the firewall.

We tried a different pdf viewer on the original laptop of the user first experiencing the problem as well as different pcs and different browsers and different versions of adobe acrobat and reader. Our network administrator is located in a remote location and she was able to view the pdfs just fine from her site. It's definitely something to do with our site, but it's figuring out what's going on with the firewall/DSL situation that's the difficult part.

We did do some capturing and are viewing with Wireshark. There seems to be a lot of duplicate acknowledgments going on. We're waiting for the Cisco engineer to get back to us with another solution, but we're starting to wonder if there could be an issue with duplexing either with our firewall or with our new hp procurve switches.
Everything is set to auto and it all says that everything is communicating 100/full duplex, but could leaving it on auto be a problem anyway?
Do you know what else could cause a lot of DUP ACKs? For instance when we make one request for a pdf the client pcs here keep opening and closing the connection to the remote server over and over as if we were making multiple requests, but we're not.
I don't think it is our adobe installations at all since this happens on several different computers with different versions of acrobat and reader having been tested. We've also tested pcs connected to different switches. Signs seem to point to the firewall being the issue since we have tried different switches. We're just not sure what the problem could be on the firewall.
Thanks everyone for your help so far!
Erin0201 :)

Dup ACKs typically means packet loss. The link may be overutilized or as you suggest duplex/speed mismatch. Always hard set links to routers and between switches. Autosense can create problems. Also check MTU settings within the devices along the path you control. This may require contacting your internet provider. I would recommend an MTU setting of no more than 1400 bytes. This will ensure that the packets leaving your network are standard size packets and don't have to get fragmented further at the network edge.

I double checked with our network administrator and our MTU settings have already been double checked and don't seem to be the problem.
The network admin says that the Cisco engineer helped her to configure the firewall to not block anything and test and we still had the issue. We haven't physically removed the firewall though, so we can't be 100% positive.
We're talking about setting our duplexing on the firewall, router, and switches all to full, but the network admin wants to wait until an evening or weekend to make sure this wouldn't cause the network to go down completely.
I tested turning the duplexing to full on just the port to my laptop from the hp switch and it caused a disconnect/reconnect, but that was it.
I won't know for awhile if setting static duplexing settings will help. We're still waiting to hear some good news from the Cisco engineer on what more he might have come up with. Is there anything else that might cause packet loss other than MTU settings and duplex speeds?
Thanks for the advice and suggestions so far everyone. Hopefully we'll get this figured out soon and it's something easy that we missed!
Erin0201 :)

We don't have a proxy, but are using OpenDNS for content filtering. The settings on OpenDNS were the first thing we looked at. Our network administrator also utilizes OpenDNS at her site and they are configured the same.

Never used OpenDNS and didn't know it offers content filtering... So googled and look what jumped-out:
...Hosting provider SoftLayer was partially taken down this morning from a DDOS attack, and several well known websites, including TechMeme and TwitPic, went down with it.
The problem at SoftLayer was resolved, but some users of OpenDNS, a DNS service provider that is becoming more and more popular, still can’t reach those websites. The reason? OpenDNS caches IP addresses for domain names on a user’s computer, and they’ve cached a bunch of bad DNS entries now on these computers. This speeds up web surfing considerably, and has helped some users avoid major outages at the ISP level in the past. But in cases like today, with outages at the hosting level, the bad IP information ends up being cached for up to a day.
Users who know what’s going on can reboot their computers to clear the cache, but that’s clearly not a good overall solution. OpenDNS says they are turning on a feature called SmartCache that caches both the current and “last good” IP address, so situations like today won’t be an issue any longer...

Thanks for the information on OpenDNS Petko!
However, both of our sites use the openDNS system and our other site isn't having the problem accessing pdfs from pdpworks. If it takes reboots of computers to clear the cache, well it's been a week since we first started having the issue and there have been several reboots.
Friday (tomorrow) we are going to set our firewall to 100 full duplex instead of auto and see if that helps at all. If not, we're going to temporarily try connecting the firewall directly to the testpc and bypass all of our switches and routers and see if the pc can connect to pdpworks and download a pdf that way. If it still doesn't work then we at least get to narrow down the problem to the firewall and/or DSL modem.
It's just weird that the user was able to get a pdf a couple of months ago from this site and now no one in the building can get one to download or open.
I'm hoping it's just the firewall since it is pretty old and has been marked for replacement soon anyway.
Thanks for the help and advice so far everyone. I'll keep you updated as to a resolution!
Erin0201 :)

An easy fix is to go into Adobe PDF Reader/Editor. Click Edit/Preferences/Internet and uncheck "Display PDF in browser" also what works most the time is to have the user right-click the link and Open in New Window.

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